This is most commonly used equipment in industries to perform desired operation with high precision and accuracy.

1. PREPARED BY
UJJWAL KUMAR CHOUBEY
UJJWALCHOUBEY@GMAIL.COM

2. Variable frequency drive (VFD)
A Variable Frequency Drive (VFD) is a type of
motor controller that drives an electric motor
by varying the frequency and voltage
supplied.
Other names for a VFD are variable speed
drive, adjustable speed drive, adjustable
frequency drive, AC drive, microdrive, and
inverter.

3. Why VFD?
As we all know, the frequency (hertz) is directly related to
the motor’s speed (RPM).
In other words, the faster the frequency, the faster the
RPM.
If an application does not require an electric motor to run
at full speed, the VFD can be used to ramp down the
frequency and voltage to meet the requirements of the
electric motor’s load.
According to application motor’s speed requirements
changes, the VFD can simply turn up or down the motor
speed to meet the speed requirement.
Hence, it is to control the motor with respect to application
and safety.

4. Circuit
The Circuit of VFD can be divided into 3 parts:
1. Rectifier
2. Filter
3. Inverter

5. Working
As shown in previous slide circuit, the VFD
begins with the 3-phase AC input supply
which go through rectifier consisting Diodes
that convert AC voltage to DC voltage.
Then after, it passes through filter which
consists of capacitors. This cleans the supply
by removing noise and passes the clean
supply to inverter.
The inverter contains transistor which
converts DC supply back AC, and send it to
the motor for operation.

6. Working
Now, about controlling of VFD. The regulator is
attached to the inverter which varies the
frequency and adjust the speed according to
application.
Also one can explore options of ramp up and
ramp down, which make sure of safe going
application.

7. Parameter and controlling
Control methods
The control capabilities can be classified into three groups:
1. Volts-per-hertz control
2. Self-sensing vector control
3. Closed-loop vector control

8. Parameter and controlling
 Volts-per-hertz control
Volts-per-Hertz (V/f) control is the most commonly
used motor control method. V/f control fixes the drive’s
output to a predefined voltage and frequency relation
for the motor to follow as the VFD’s speed command is
adjusted.
V/f control is commonly used for systems that do not
require precise speed control, such as fans or pumps.
The slight change in speed does little to impact the
overall system performance as other drive
programming will adjust the speed to maintain system
demand.

9. Parameter and controlling
 Self-sensing vector control
Self-sensing vector control is a control method that
provides fine-tuned control of the motor’s speed. The
complicated algorithms are used to monitor, interpret
and respond to current feedback to provide precise
motor control.
Self-sensing vector control methods improves process
control and reduces maintenance. This control regulates
motor speed within 1/200th of motor rated speed,
provide dynamic speed control, also limits current and
torque without external devices. The VFD requires specific
motor information, such as motor no-load current,
resistance, and inductances to provide this motor control.

10. Parameter and controlling
 Closed-loop vector control
Closed-loop vector control is the most advanced motor
control method. The closed-loop vector control uses a
motor encoder to provide precise speed feedback and
eliminate any error in VFD control responding to current
feedback.
Closed-loop vector control’s add speed feedback signal to
maximize process control and minimize maintenance. This
allows for precise speed control down to one RPM, high
starting torque at zero speed, zero speed control, and
torque regulation.

11. Parameter and controlling
Acceleration and deceleration times
A VFD starts and stops the motor based on programmed
acceleration and deceleration times. These times or ramp rates
define how long the drive will take to get from zero to
maximum frequency.
Based on the inertia of the load, it is possible to start/stop a
load quicker than what allowed based on the current
capabilities of the motor. Aggressive acceleration/deceleration
rates will lead to higher currents that may max the drive and
motor and lead to overload or overcurrent faults. Setting the
correct acceleration and deceleration time ensures proper
system performance while ensuring no fault operation.

12. Parameter and controlling
Speed and run source
A VFD requires two things at every moment of its
operation: a run command and speed reference. The run
command tells the drive it should operate the motor, while
speed reference tells the VFD what frequency to run.
Setting the VFD’s speed and run command is more about
how one chooses to run the motor. Each source has its
own benefit: A voltage reference is simple to generate and
easy to understand, while current signals propagate longer
distances and being easily affected by nearby electrical
noise, other avenues of control are through direct keypad
or via network communications.

13. Parameter and controlling
Fault Reset
To maintain product lifetime and prevent failure,
VFDs incorporate and trigger faults to protect
themselves.
Many VFDs incorporate automatic fault reset
capabilities. This feature allows the drive to detect a
condition outside the scope of its programming and
trigger a fault to protect itself, the motor, and the
rest of the mechanical system. The purpose of the
auto reset is to overcome nuisance faults and
maintain continuous operation.

14. Advantages
 Keeps starting current in control
 Helps in controlling operating speed
and acceleration
 Limits and adjusts torque
 Saves energy and cost

15. Disadvantages
 Upfront cost of a VFD can be relatively high
depending on how large your system is.
 Dramatically increased noise
 Excessive vibration
 Can reduce the service factor on the motor
it’s used on